Rare earth activated alkaline earth halofluoride luminescent materials



United States Patent Ofifice 3 l 63 ,6 l Patented Dec. 29, l 964 This invention relates to novel luminescent materials which are particularly, but not necessarily exclusively, useful as laser materials.

Laser materials and systems are described by Vogel et al. in Electronics, October 27, 1961, pages 40 to 47. The word laser is a short form for light amplification by stimulated emission of radiation. Laser materials are luminescent materials which exhibit stimulated emission of radiation under a particular set of conditions. When a material exhibits a stimulated emission of radiation, it is said to lase. A laser material is usually a single crystal body comprised of a matrix material having impurity ions or dopants contained therein. The desirable characterteristics of a laser material result from the com bination of matrix material, dopant, and cr'ystallinity of the material. 7

An object of this invention is to provide novel luminescent materials.

A further object is to provide novel laser materials.

In general, the luminescent materials of the invention have a tetragonal crystal structure and the molar composition:

AHaFzyM Where:

A is at least one of Ba, Ca, and Sr Ha is at least one of Cl, Br, and I M is at least one of Sm, T111 and U y is between about and 10- mol.

When excited with suitable radiant energy, the foregoing materials luminesce, emitting radiation in vrelatively narrow bands, generally in the red and infrared regions of the spectrum. This luminescence occurs with the material at room temperature and at liquid nitrogen temperatures. The wavelength ranges of emitted radiation is related to the dopant. For divalent samarium Sm+ the range is about 5500 to 8500 A. For trivalent uranium U+ .the range is about 8000 to 25000 A. For divalent thulium' Tm, the range is about 10,000 to 12,000 A. Generally, the emission bands are shifted toward the shorter Wavelengths when higher molecular weight A and Ha are selected. When the materials of the invention are prepared in single crystal form with high purity and crystallinity, at least some of the crystals can be made to lase with radiant excitation.

The following are some typical luminescent compositions of the invention:

BaClF 0.00007Sm The luminescent materials of the invention may be prepared by fusing together pure anhydrous constituent halides in atmospheres which are conducive todeveloping the desired valency in the dopant. Typically, one mol anhydrous AHa one mol anhydrous AF and the desired mol proportion of MHa or MF are fusedtogether composition BaClF:0.001U+ or ultraviolet excitation, the material luminesceslat room in a reducing atmosphere, such as hydrogen; or a neutral atmosphere, such as nitrogen, argon, or neon, or combinations thereof. The dopant may be introduced as an oxide of M provided the atmosphere contains also the corresponding hydrogen halide. The melt is then solidified by cooling to room temperature in the atmosphere. The AHa and the AF may be combinations of two or more different halides.

The AHa ,.AF MHa, and MF are preferably substantially free of carbonaceous material, free Water, and chemically-combined water. Some reagent grade raw materials satisfy these requirements and some do not. Suitable CaCl may be prepared from unsuitable reagent grade CaCl as follows: Hydrated CaCl is-dried at 200 C. in air, then is melted under a dry HCl atmosphere, and then is cooled. The solidified melt is dissolved in water and filtered. The filtrate is evaporated and'the remaining solids aredried in air at 200 C. The dry solids are remelted under a dry HCl atmosphere, and the melt solidified to produce the purified raw material. BaCl and Cal BaBr Bal SrBr and Sri may be prepared by the same technique except that HBr or HI atmospheresare substituted for HCl when preparing the bromides and iodides respectively. .Direct combination of the metal and halogen can also be used as ameans of preparation.

Example 1.Mix 1.0 x 10" mol Sm O with one mol pure anhydrous CaCl Melt the mixture in a dry atmos phere containing about equal parts by volume of hydrogen and HCl. The proportions in parts by volume of H /HCl may be between /10 and 20/80. Solidify the melt and add one mol pure anhydrous CaF Melt the mixture in an atmosphere of dry hydrogen and then solidify to form a luminescent material having a tetragonal crystal structure and the formula With visible or ultraviolet excitation, the material luminesces at wavelengths of about 6945 A., 7075 A., and 7355 A.

.Example 2. To prepare SrClF:0.001Sm+ follow the procedure of Example 1 except substitute SrCl -for CaCl and SrF for CaF With visible or ultraviolet excitation, the material luminesces at wavelengths of 6435 A., 6905 A., and 7310 A. q

Example 3.Mix 2.0 x 10- mol U1 (or U0 with one mol pure anhydrous BaCl of hydrogen and HCl and then solidify the melt. To thesolidified melt, add one mol pure anyhdrous BaF Melt this mixture in an atmosphere of dry hydrogen gas and then solidify the melt to produce a luminescentmaterial having a tetragonal crystal structure and the molar temperature at wavelengths of'about 2.420 micron, 1.410 micron, .870 micron. i v 7 Example 4.Mix 0.5 x 10* molTm' O with one mol pure anhydrous BaBr Melt the mixture in a dry atmos- L pherefcontaining about equal parts by volume hydrogen Melt the mixture in ;a dry'atrnosphere containing about equal parts by volume With infrared, visible,-

3 and HBr and then solidify the melt by cooling. To the solidified material, add one mol BaF and 0.5 x mol thulium metal powder. Melt this mixture in a dry atmosphere of hydrogen (or helium or argon) and then solidify the melt to produce a luminescent material having a tetragonal crystal structure and the molar composition BaBrF:0.001Tm+ With infrared, visible, or ultraviolet excitation, the material luminesces at room temperature at wavelengths of about 1.151 micron and 1.160 micron. The luminescent materials of the invention may be prepared as relatively large single crystals with a high degree of crystallinity. This may be achieved by melting the luminescent materials of the invention and growing crystals thereof by the Bridgman technique, either horizontal or vertical. The horizontal Bridgman technique is preferred. In one application of the Bridgman technique, a quantity of material is passed through two zones, one of which is maintained about 20 C. above the melting point of the material and the other of which is maintained at temperature about 20 C. below the melting point of the material. A rate of travel of about one inch er 24 hours has been found to be adequate. Large single crystals may also be grown by the Czochralski method.

What is claimed is:

1. A luminescent material having a tetragonal crystal structure and the molar composition:

AHaFzylll where: A is at least one of the group consisting of Ba, Ca, Sr Ha is at least one of the group consisting of Cl, Br, I F is fluorine M is at least one of the group consisting of Sm+ T111 and U+ y is between about 10- and 10" 2. A luminescent material having a tetragonal crystal structure and the molar composition:

BaHaFzyM where: Ha is at least one of the group consisting of Cl, Br, and I M is at least one of the group consisting of Sm Tm,

and U+ y is between about 10- and 10' 3. A luminescent material having a tetragonal crystal structure of the molar composition:

CaHaF yM where: Ha is at least one of the group consisting of Cl, Br, and I M is at least one of the group consisting of Sin, Tm

and U+ y is between about 10- and 10' 4. A luminescent material having a tetragonal crystal structure and molar composition:

where: Ha is at least one of the group consisting of Cl, Br, and I M is at least one of the group consisting. of Sm, Tm+

and U+ I y is between about 10-- and 10*- 5. A luminescent material having a tetragonal crystal structure and the molar composition:

CaClFzySm+ where: y is between about 10 and 10" 6. A luminescent material having a tetragonal crystal structure and the molar composition:

SrClF2ySm+ where: y is between about 10- and 10- 7. A luminescent material having a tetragonal crystal structure and the molar composition:

BaClFyU+ where: y is between about 10 and 10- 8. A luminescent material having a tetragonal crystal structure and the molar composition:

BaBrFzyTm where: y is between about 10- and 10- 9. A luminescent material having a tetragonal crystal structure and the molar composition:

BaClFzySm+ where: y is between about 10- and 10- References Cited by the Examiner UNITED STATES PATENTS 2,303,963 12/42 Uhle 252301.4 2,409,174 10/46 Dietz 252301.4

OTHER REFERENCES Kroger: Some Aspects of the Luminescence of Solids, Elsevier Pub. Co. Inc., N.Y., 1948, pages 283, 284, 294- 296 and 298.

MAURICE A. BRINDISI, Primary Examiner.

JULIUS GREENWALD, Examiner. 

1. A LUMINESCENT MATERIAL HAVING A TETRAGONAL CRYSTAL STRUCTURE AND THE MOLAR COMPOSITION: 